Nobody bought the IBM PC because it was called a "PC". They bought it because it was IBM, and in the 1980s there was a saying: "Nobody ever lost their job buying IBM".
Yes, that's right. What I'm saying is that IBM successfully sold the term "IBM PC" because it contained the magic letters I-B-M. But then the magic slowly spread to the other half of the phrase IBM PC, to the point where PC eventually became synonymous with IBM.